Mobility and Fate of Asbestos Particles in the Environment: Minimizing the threat that asbestos disposal sites present to surrounding communities requires containment; preventing offsite migration is of paramount importance. Because asbestos fibers are most hazardous when inhaled, research has focused on airborne transport. However, there is now ample empirical evidence that aqueous transport - in groundwater and rivers - is a significant pathway for spreading of asbestos, and such transport has threatened drinking water supplies in some areas. Because asbestos particles have a large specific surface area, surface charge effects are strong and presumably influence their mobility and interaction with the environment. In particular, asbestos fibers rarely exist in isolation but rather form aggregates; however, little is known regarding the mechanisms controlling aggregate formation. In addition, the unusually large aspect ratio of asbestos is expected to exert a strong control on the migration and trapping of particles in groundwater transport through soil; however no studies have examined aqueous transport in the laboratory. We hypothesize that aggregate size exerts the primary control on the rate of trapping of asbestos particles in soil, and that such trapping (straining) may reversed under changing water chemistry. We propose to test these hypotheses with three Specific Aims. Aim 1: To elucidate the physico-chemical processes controlling asbestos aggregate formation and mobility. Aim 2: Determine mobility and straining of asbestos in groundwater, through laboratory experiments and theory. Aim 3: To identify the extent of groundwater transport, and the size distribution of aggregates, for asbestos particles at the Ambler Superfund site; and make recommendations for containment of asbestos to limit aqueous transport. Our key innovations are to: (1) probe the dynamics of asbestos at the fiber scale using real-time electron-microscopy observations; (2) perform innovative soil column experiments that allow us to image the internal granular pore structure; and (3) apply experimentally-validated theories to field observations at a Superfund site to make scientifically-informed recommendations for improving containment strategies of asbestos. We believe that the proposed research will directly inform policy for asbestos containment at Superfund and Brownfields sites, while bringing immediate benefit to the community surrounding the Ambler asbestos piles.